1. Field of the Invention
The present invention relates to a stereoscopic image photographing optical system and a stereoscopic image photographing apparatus having the optical system, which are adapted to obtain a stereoscopic image by leading images having parallax for right and left eyes (parallactic images) alternately in a time-series manner to one image sensor with shutter means.
2. Description of Related Art
In recent years, there have been proposed a variety of stereoscopic image display apparatuses for observing stereoscopic images. For example, there is known a stereoscopic image display apparatus in which right and left parallactic images are displayed on a monitor and are observed by the observer with liquid-crystal shutter spectacles. In such a stereoscopic image display apparatus, the states of right and left liquid crystal elements of the liquid-crystal shutter spectacles are synchronized with an image signal. More specifically, during the period when an image for the right eye is being displayed on the monitor, the liquid crystal element for the right eye is set to a transmissive state and the liquid crystal element for the left eye is set to a non-transmissive state, while, during the period when an image for the left eye is being displayed on the monitor, the liquid crystal element for the right eye is set to a non-transmissive state and the liquid crystal element for the left eye is set to a transmissive state. By this arrangement, when an image for the right eye and an image for the left eye are alternately displayed on the monitor, the observer is enabled to view an image for the right eye always with the right eye and an image for the left eye always with the left eye. Accordingly, a stereoscopic image giving a sensation of depth is observed by the observer.
Further, in recent years, a display of the head-mounted type or the spectacle type, i.e., the so-called head-mounted display, has been developed. In the head-mounted display, too, images for the right eye and for the left eye are selectively displayed for the right eye and the left eye, respectively, so that the observer is enabled to view a stereoscopic image giving a sensation of depth.
In addition, there has been proposed, in Japanese Laid-Open Patent Applications No. Hei 9-311294, No. Hei 9-311295, No. Hei 9-318911 (corresponding to U.S. Pat. No. 6,061,179), etc., a stereoscopic image observing apparatus in which a liquid crystal display is combined with a lenticular sheet having minute lenses of a predetermined pitch or with a mask having a predetermined pattern of aperture parts and non-aperture parts. In such a stereoscopic image observing apparatus, light beams from the liquid crystal display are made to have directivity, and the directivity is made to match with an image pattern displayed on the liquid crystal display, so that an image for the right eye is observed with the right eye and an image for the left eye is observed with the left eye, thereby enabling the observer to view a stereoscopic image giving a sensation of depth.
In order to observe a stereoscopic image, it is necessary to produce a plurality of parallactic images. Heretofore, there have been proposed a variety of stereoscopic image photographing optical apparatuses or stereoscopic image photographing optical systems for obtaining a plurality of parallactic images.
Heretofore, in the above-mentioned stereoscopic image photographing apparatus, it is general that a plurality of parallactic images to be displayed are picked up by the twin-lens type stereoscopic camera having two lenses (photographic lenses).
In addition, there has been proposed a camera which does not require two photographic lenses (a photographing apparatus for stereoscopic television disclosed in Japanese Patent Publication No. Hei 8-27499). This camera has two liquid-crystal shutters, a total-reflection mirror and a half-reflection mirror, and is arranged to pick up right and left parallactic images alternately through one photographic lens.
Further, in the case of the twin-lens type stereoscopic camera, the so-called convergence adjustment for adjusting the parallax of right and left parallactic images during photographing is required for the photographic lenses for time-divisionally picking up right and left parallactic images. Heretofore, in general, the convergence adjustment is performed manually.
Since, in the case of the above-mentioned conventional twin-lens type stereoscopic camera serving as an apparatus for obtaining parallactic images for the right eye and the left eye, an image for the right eye and an image for the left eye are picked up for the respective photographic lenses, if the difference between the two photographic lenses in optical performance, such as magnification, deviation of an optical axis, color, brightness, distortion, field tilt or the like, occurs due to the manufacturing error of photographic lenses, the observer tends to feel tired in viewing a stereoscopic image, or two images tend to be unable to fuse with each other. Accordingly, it is necessary to heighten the accuracy of parts so as to match the optical performance of one lens with that of the other lens, or it is necessary to make the adjustment of parts if the increased accuracy of parts is still insufficient for optical performance. Further, in order to absorb the difference in optical performance, it is necessary to take special measures, such as an electrical correction of images.
Further, in a case where zoom lenses are used as the photographic lenses, the magnification varying actions of two, right and left, photographic lenses are required to interlock with each other during zooming with the optical performance of each lens adjusted. Therefore, the twin-lens type stereoscopic camera having zoom lenses becomes complicated in mechanism, and necessitates a time-consuming job for manufacturing and has low mass-productivity.
In addition, two monitors are naturally needed for observing images picked up by the twin-lens type stereoscopic camera, so that the practicability thereof is little. Further, if such two images are to be recorded, it becomes necessary to record two image signals in the state of being synchronized with each other. Therefore, a special recording apparatus is needed. Further, in order to avoid this arrangement, it is conceivable to convert two image signals into one image signal. However, for that purpose, there is needed a special converter for use in displaying and recording right and left parallactic images alternately.
Accordingly, the twin-lens type stereoscopic camera has a large camera body as compared with that of the ordinary single-lens type camera, and the whole system thereof necessitates a special apparatus, as mentioned in the foregoing. Therefore, the twin-lens type stereoscopic camera is large in size, and has low mobility, so that it has been difficult to widely spread the twin-lens type stereoscopic camera into the world.
On the other hand, the camera proposed in the above-mentioned Japanese Patent Publication No. Hei 8-27499 has such a drawback that, since optical paths of parallactic images for the right and left eyes are combined by the half-reflection mirror to be lead to the photographic lens, the amount of light of an image incident on the photographic lens after being transmitted or reflected by the half-reflection mirror becomes half. Further, in the construction of the camera disclosed in the above-mentioned Japanese Patent Publication No. Hei 8-27499, theoretically, the optical path lengths of parallactic images for the right and left eyes are different from each other, so that a difference in magnification between the parallactic images for the right and left eyes would occur. This causes the fatigue of the observer in observing an image picked up by the above-mentioned camera, or makes it impossible for two parallactic images to fuse with each other for a stereoscopic viewing.